The present invention is directed to sedimentation apparatus and more particularly to apparatus for clarification of liquids by separation of a solids from a liquid solids suspension wherein flocculants are added to the suspension for increasing the rate of separation and providing a dense underflow.
In certain sedimentation apparatus which comprise cylindrical settling tanks which utilize central feedwells for receiving a solids contained liquid suspension for settling the solids within the tank, it is well known to utilize the addition of flocculating chemicals to the influent either in the feedwell or at a point prior thereto to promote the agglomeration of solids and rapid settling thereof within the tank. The settled solids form a dense underflow and are removed from the bottom of the tank by means of rotating rake means which direct the settled mass to a central discharge sump in the tank. Simultaneously the clarified liquid overflows the top of the tank into a peripheral launder. Various means are utilized for introducing the settling solids from the feedwell either directly into the dense underflow bed or into a settling zone above the bed and for controlling the amount of flocculant dosage in accordance with a selected desired rate of settling.
In flocculation treatment utilizing equipment of the aforementioned type where the treatment of the influent is effected within the confines of the feedwell it is important that the flocculant be added to the influent in such a manner so as to obtain maximum distribution of the flocculant throughout the feedwell to form flocs in a rapid manner for settlement in the feedwell without further disturbing effects. It is therefore essential that a rapid and efficient mixing of flocculant with the influent feed be effected.
In the past various means have been employed for accomplishing these desired results by locating a flocculant feed means within a feedwell. For example in the apparatus disclosed in U.S. Pat. No. 3,532,218 a sparger ring is located about the upper periphery of a deep feedwell and which sparger is provided with orifices for introducing a flocculant into the feedwell for mixture with the influent feed. In U.S. Pat. No. 4,054,514 an auxiliary mixing tank is located within the main feedwell and is provided with an agitating device for mixing and dispersing flocculant treated feed suspension as an overflow from the auxiliary tank into a main feedwell. On the other hand U.S. Pat. No. 2,528,094 discloses an arrangement wherein a flocculant is introduced into a tank to mix with the influent with a series of baffles provided to mix the flocculant with the influent feed.
The aforementioned prior art devices have met with varying success and do not exhaust the various prior art means for mixing flocculant either in or exterior to a feedwell but illustrate generally the prior art attempts to provide such means. Various problems are encountered in known devices in effectively and efficiently accomplishing the rapid settlement of solids. In one known type feedwell structures as disclosed in U.S. Pat. No. 3,006,474 a feedwell is disclosed which comprises a feed distributor unit comprising circular channels or raceways juxtaposed one upon the other within a cylindrical feedwell. The main influent feed stream is split into two separate streams which are fed into the channels tangentially with one stream rotating counterclockwise and the other clockwise. The streams are displaced inwardly in opposite directions from the channels and are compelled to shear in a plane along the entire length of the channel at twice the velocity of either stream. The kinetic energy of the stream is thereby converted to a random turbulence of small eddies resulting in the elimination of any residual tangential velocity components to effectively dissipate the energy of the influent feed. This type feedwell has met with widespread acceptance and in view of the lack of moving parts is an economical and effective device.
It is an object of the present invention to provide a sedimentation device wherein novel means are included for introducing and mixing flocculant chemicals with an influent solids containing feed stream whereby the latter are mixed rapidly and thoroughly.
Another object is to provide for a novel flocculant distributor means for promoting a rapid agglomeration of settling solids within a feedwell resulting in dense underflow and a clarified overflow.
A still further object is to provide novel means for introducing flocculant in a feedwell for effective and rapid separation of solids from a liquid suspension without the use of complex structure or moving parts.